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<title>WebGL - Multiple Objects</title>
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<div class="description">
Uses a few utility functions so there's much less code.
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<canvas id="canvas"></canvas>
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<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<script src="resources/webgl-utils.js"></script>
<script src="resources/m4.js"></script>
<script src="resources/primitives.js"></script>
<!-- vertex shader -->
<script id="vertex-shader-3d" type="x-shader/x-vertex">
attribute vec4 a_position;
attribute vec4 a_color;

uniform mat4 u_matrix;

varying vec4 v_color;

void main() {
  // Multiply the position by the matrix.
  gl_Position = u_matrix * a_position;

  // Pass the color to the fragment shader.
  v_color = a_color;
}
</script>
<!-- fragment shader -->
<script id="fragment-shader-3d" type="x-shader/x-fragment">
precision mediump float;

// Passed in from the vertex shader.
varying vec4 v_color;

uniform vec4 u_colorMult;

void main() {
   gl_FragColor = v_color * u_colorMult;
}
</script>
<script>
"use strict";

function main() {
  // Get A WebGL context
  /** @type {HTMLCanvasElement} */
  var canvas = document.querySelector("#canvas");
  var gl = canvas.getContext("webgl");
  if (!gl) {
    return;
  }

  // creates buffers with position, normal, texcoord, and vertex color
  // data for primitives by calling gl.createBuffer, gl.bindBuffer,
  // and gl.bufferData
  const sphereBufferInfo = primitives.createSphereWithVertexColorsBufferInfo(gl, 10, 12, 6);
  const cubeBufferInfo   = primitives.createCubeWithVertexColorsBufferInfo(gl, 20);
  const coneBufferInfo   = primitives.createTruncatedConeWithVertexColorsBufferInfo(gl, 10, 0, 20, 12, 1, true, false);

  // setup GLSL program
  var programInfo = webglUtils.createProgramInfo(gl, ["vertex-shader-3d", "fragment-shader-3d"]);

  function degToRad(d) {
    return d * Math.PI / 180;
  }

  var cameraAngleRadians = degToRad(0);
  var fieldOfViewRadians = degToRad(60);
  var cameraHeight = 50;

  function computeMatrix(viewProjectionMatrix, translation, xRotation, yRotation) {
    var matrix = m4.translate(viewProjectionMatrix,
        translation[0],
        translation[1],
        translation[2]);
    matrix = m4.xRotate(matrix, xRotation);
    return m4.yRotate(matrix, yRotation);
  }

  requestAnimationFrame(drawScene);

  // Draw the scene.
  function drawScene(time) {
    time *= 0.0005;

    webglUtils.resizeCanvasToDisplaySize(gl.canvas);

    // Tell WebGL how to convert from clip space to pixels
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

    gl.enable(gl.CULL_FACE);
    gl.enable(gl.DEPTH_TEST);

    // Clear the canvas AND the depth buffer.
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    // Compute the projection matrix
    var aspect = gl.canvas.clientWidth / gl.canvas.clientHeight;
    var projectionMatrix =
        m4.perspective(fieldOfViewRadians, aspect, 1, 2000);

    // Compute the camera's matrix using look at.
    var cameraPosition = [0, 0, 100];
    var target = [0, 0, 0];
    var up = [0, 1, 0];
    var cameraMatrix = m4.lookAt(cameraPosition, target, up);

    // Make a view matrix from the camera matrix.
    var viewMatrix = m4.inverse(cameraMatrix);

    var viewProjectionMatrix = m4.multiply(projectionMatrix, viewMatrix);

    // Our uniforms. In this case we only have one, "u_matrix" which we'll see below
    var uniforms = {
    };

    // ------ Draw the sphere --------

    gl.useProgram(programInfo.program);

    // Setup all the needed attributes.
    webglUtils.setBuffersAndAttributes(gl, programInfo, sphereBufferInfo);

    uniforms.u_matrix = computeMatrix(viewProjectionMatrix, [0, 0, 0], time, time);

    // Set the uniforms we just computed
    webglUtils.setUniforms(programInfo, uniforms);

    gl.drawArrays(gl.TRIANGLES, 0, sphereBufferInfo.numElements);

    // ------ Draw the cube --------

    // Setup all the needed attributes.
    webglUtils.setBuffersAndAttributes(gl, programInfo, cubeBufferInfo);

    uniforms.u_matrix = computeMatrix(viewProjectionMatrix, [-40, 0, 0], time, -time);

    // Set the uniforms we just computed
    webglUtils.setUniforms(programInfo, uniforms);

    gl.drawArrays(gl.TRIANGLES, 0, cubeBufferInfo.numElements);

    // ------ Draw the cone --------

    // Setup all the needed attributes.
    webglUtils.setBuffersAndAttributes(gl, programInfo, coneBufferInfo);

    uniforms.u_matrix = computeMatrix(viewProjectionMatrix, [40, 0, 0], -time, time);

    // Set the uniforms we just computed
    webglUtils.setUniforms(programInfo, uniforms);

    gl.drawArrays(gl.TRIANGLES, 0, coneBufferInfo.numElements);

    requestAnimationFrame(drawScene);
  }
}

main();
</script>
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